Using PermissionsEx and WorldGuard, do you have any suggestions on how I might retroactively flag hundreds of people for a world guarded region using an existing permission? I wanna give like 400+ people access to specific regions but I am unsure how to do that efficiently.

Use Groups. "Sometimes, it may be desired for a flag to only apply to a certain group of players rather than everyone that should enter the region. This can be achieved by specifying an additional “region group” when defining the flag, of which there are several options:

all (everyone)
members
owners
nonmembers
nonowners
The group can be specified using the -g marker as illustrated below:

/region flag spawn -g nonmembers pvp deny
It is not possible to set the same flag to different values for more than one group on the same region. If you need that functionality, consider making several regions." From: https://worldguard.enginehub.org/en/latest/regions/flags/
p.s. The correct term is recursive.

Alright thanks for the quick read-over. The only question/issue i have is the fact that since Mudge originally replied to the application i thought that meant he/she would be the one handling it so i don't know why you are the one declining it?

Use Groups. "Sometimes, it may be desired for a flag to only apply to a certain group of players rather than everyone that should enter the region. This can be achieved by specifying an additional “region group” when defining the flag, of which there are several options:

all (everyone)
members
owners
nonmembers
nonowners
The group can be specified using the -g marker as illustrated below:

/region flag spawn -g nonmembers pvp deny
It is not possible to set the same flag to different values for more than one group on the same region. If you need that functionality, consider making several regions." From: https://worldguard.enginehub.org/en/latest/regions/flags/
p.s. The correct term is recursive.

This is exactly what I would do, the question is how to I add 400+ people to it based on pre-existing permissions already stored in pex?